These are the heaviest (and therefore essential) black metal albums that come to my mind:
1349 – BEYOND THE APOCALYPSE (2004)
This is heavy and aggressive as fuck. I can hardly listen to the whole album without interruption because the inhuman rawness makes my ears bleed and the skin peel off my skull. This must have been the soundtrack of Lucifer being cast down to hell. It's completely incomprehensible to me how human beings can record that kind of music. It's fucking beautiful.
Anaal Nathrakh – HELL IS EMPTY AND ALL THE DEVILS ARE HERE (2007)
Anaal Nathrakh ate just another band whose sound is considered overproduced by a broad majority of black metal purists because they dare to sound awesome instead of shitty. What you get here is truly a "pandemonic hyperblast". If you don't start to shiver in fear and anticipation of what's going to come next at the first sounds of the intro, you're either deaf and need to turn the sound so fucking far up that the ensuing blastbeats make the floor tremble, or your head is so far up your asshole you're tasting your gastric juice. According to this album, the apocalypse will be a lot worse than the very worst you can imagine. The feat that the band achieved here was to turn that unleashed boundless violence into not just listenable songs, but real killer songs with nipple hardening riffs and a sound so opulent it seems almost artificial. And adding the grindcore elements was a real stroke of genius – the abysmally deep death grunts paired with the abattoir-like screeching kill 'em all. All. Best song: probably "Until the World Stops Turning". The beginning with the machine gun fire mixed with the drumming is enough to make me cum instantly.
Nattefrost – BLOOD AND VOMIT (2004)
The album title alone justifies its mention in this list. The music follows along, primitive, raw and loud as can be. It's probably the most primitive-aggressive album ever recorded. The beat is almost techno, which, strangely, makes it even more evil. It's even loud if you turn the sound down. And did anyone before Nattefrost have the idea incorporate distorted puking sounds into his music? I just wonder why Nattefrost is so fucking pissed. The album sounds like he poured boiling water over his dick while he recorded it. Or maybe he realized that if you invert an inverted cross it looks like a latin cross. Don't listen to this record in public places, because you will look pretty strange trying to keep a decent expression on your face, while the wrath of Nattefrost slits your guts and fists your ass.